You can find out if it's on the market by calling any Realtor.
The Realtor probably can find out the answer as to why it can't be shown.
A Realtor can also tell you how many days the property has been on the market. Or try checking Zip Realty ( http://www.ziprealty.com ) That site tells you how long the property has been on the market and what price reductions, if any, have been taken.
Hope that helps.